Since the discovery of single walled carbon nanotubes almost twenty years ago, there has been much interest in their use as electronic circuit elements. Applications ranging from field effect transistors (“FETs”) to chemical sensors to flow meters have been explored. The most common method for fabricating single walled carbon nanotube circuits since their inception has been electron beam lithography. One drawback to electron beam lithography is that it is a serial process. As such, the production of large arrays of devices or complex circuits requires a system to run for hours, possibly days, at a time. This is both time consuming and costly. By contrast, photolithography has been a standard processing technique in the production of complementary metal-oxide semiconductor (CMOS) processing since the 1960's and its parallel nature allows for wafer scale production of circuits in a matter of seconds.
To date, all attempts to use photolithographically defined carbon nanotubes have reported several problems. One method of incorporating carbon nanotubes into such devices has been to photolithographically define leads onto a substrate, and subsequently grow the carbon nanotubes across the leads allowing for devices. This provides for a so-called “side contact” geometry, wherein the carbon nanotubes essentially rests on the surface of the metal contacts. The resulting electrical contacts are inferior, owing to the reduced contact areas. A more desirable mode of contact is to first deposit the carbon nanotube onto the surface and, following photolithographically defining the metal circuit traces, deposit the metal onto the carbon nanotubes. This results in an electrical contact, known as an “end contact” wherein the metal contacts conform all around the ends of the carbon nanotubes. Unfortunately, practitioners of this method report the formation or presence of what is believed to be a residual “scum” layer resulting from the use of conventional photoresists. There exists a need to develop methodologies which provide for end contact connections of nanotubes which do not suffer from the problems associated with residual photoresist processing scum.